Present Liquid Level measuring devices that are similar to this invention utilize a resistive type probe and rely on the change of resistivity of the probe with temperature. A significant decrease in the resistivity of the probe over its value when it was measured in air indicates that the probe is submerged in liquid. Devices that rely on change in resistivity are usually only capable of determining whether or not a certain level, such as the location of the probe, is reached. Even when several probes are used, liquid levels can only be determined at discrete locations of the probe. Intermediate levels between two probes can not be determined. Resistive probes are only accurate at the temperatures in which they are calibrated. They need to be re-calibrated at other operating temperatures. Furthermore, resistive probes usually require compensating resistors or circuits, resulting in a network that is susceptible to electromagnetic interference or electrical noise from other electrical/electronic equipment within its vicinity.
This invention precludes the shortcomings inherent in liquid level devices employing resistive probes, because actual temperature are used and processed, and the temperatures measured are dependent on heat transfer mechanisms rather than change in resistivity of the probe material. Furthermore, the invention is capable of not only determining liquid level at discrete points where the temperature sensors are located, but can also measure liquid levels at intermediate points between two temperature sensor locations, which the resistive type device is incapable of doing.
The heat transfer mechanism creates a voltage or a temperature profile along a heater. This profile is used to determine the discrete and continuous liquid level. In the prior art, U.S. Pat. No. 2,279,043 Harrington used heated liquids in a container to determine the discrete liquid levels with a set of discrete thermocouples. In U.S. Pat. No. 3,279,252 Barlow used heated cylinder to determine the discrete liquid levels. In U.S. Pat. Nos. 5,730,026 and 5,908,985 Maatuk used a separate heated Nichrome wire and a strip to determine the continuous and discrete liquid levels.
In this invention, a method is presented to create a desired profile along a heater that is also used as a common wire for a set of discrete thermocouples. In other words, the separate heater is eliminated and instead, the common wire of the thermocouple set is also used as the heater.
In U.S. Pat. No. 4,573,128 Wilson and U.S. Pat. No. 4,573,128 Mazur used a poured molted liquid in a container to obtain a profile and measure the liquid level in a container. In this invention, I apply heat to the surface of a wire to obtain a profile along the wire,
This invention also detects ice on a surface by looking at a phase change effect (xe2x80x9cIglooxe2x80x9d) and temperature profile. In U.S. Pat. No. 5,521,584 Ortolano detect ice by measuring heat flow and heat measurement.
The invention described herein is a means of measuring the level of a liquid in a liquid container such as a fuel tank by means of a probe to which heat is applied and the temperature along the length of the probe is measured. This invention makes use of the difference in cooling efficiency between liquid and gas such as air, or between two different liquids, such as water and oil. When heat is applied to the probe, the temperature of the portion of the probe submerged in liquid is significantly lower than the temperature of that portion of the probe outside of the liquid and typically exposed to air. This is because the liquid removes heat at faster rate than air, so that the temperature difference between the surface of the probe is much lower in liquid than it is in air. This is also true between a liquid that removes heat more efficiently, such as water, and a liquid that does not remove heat as efficiently, such as oil. Temperature sensors, such as thermocouples or thermistors that are attached to various points on the probe measure the temperatures at those respective locations on the probe. This invention is not only capable of determining where the liquid level is at discrete points where the temperature sensors are attached. It can also determine where the liquid level is between two discrete points to within a fraction of centimeter accuracy, when precision temperature measurement devices are used in conjunction with suitable microprocessor, which process the signals received from the temperature sensors.
The purpose of this invention is to provide a device that can measure liquid levels, such as that of fuel in an automobile fuel tank or lubrication oil level in an automobile engine compartment fairly accurately and with minimal effort, such as simply pushing a button on an instrument panel, as shown in FIG. 1. The advantages of this invention are (1) It can measure liquid levels accurately, within a fraction of a centimeter; (2) It requires a very small amount of power to operate; (3) It is compact and light weight and can be installed in relatively small liquid containers if necessary; (4) It is reliable since it has no moving parts; (5) because it requires a very small power for operation, it does not generate any significant amount of electromagnetic energy which could interfere with the performance of other electrical/electronic equipment; and (6) with certain modifications to the device, it can be used to measure other important liquid parameters such as viscosity and density. This device can also be adopted for the detection of ice formation on the external surface of an aircraft, such as the external surface of an aircraft wing or fuel tank.